1. Field of the Invention
This invention relates to rotary drum strainers and particularly to rotary drum strainers that are self-cleaning.
2. Description of Related Art
Strainers are used in association with motor-driven pumps that suck water out of outdoor pits, reservoirs, streams, ponds, and the like, for mining, irrigation, or watering purposes. Typically, strainers are connected to pumps by a long intake conduit or hose that extends from the strainer in the body of water to a pump on land. Strainers are placed on the end of the intake to prevent debris, small stones and other objects from being sucked into the pump while pumping. As a pump is operated, the strainer may be covered with leaves and other large pieces of debris that are drawn to the strainer. This material eventually blocks the strainer openings, thereby reducing the flow of water through the strainer, possibly even shutting it off entirely. Once plugged, the strainer must be removed from the water and cleaned. During this time, no water can be pumped. Depending on the water source, this cleaning operation can be frequently required, making the pumping operation inefficient.
To overcome this problem, self-cleaning strainers have been developed. For example, U.S. Pat. Nos. 5,275,656, 5,108,592, and 4,822,486 use water fed from the pressure side of the pump to rotate and clean the screen. This water washes debris from the screen while the pump is in operation. However, the volume of water delivered to a pump is reduced using this method because some water is redirected to the strainer. Moreover, this method of cleaning and rotating the screen depends on pump pressure being high enough to effectively clean and rotate the screen. Finally, although the devices clean the strainer, the debris removed from the strainer remains in the body of water near the strainer. This debris is then pulled right back onto the strainer where it must be washed off again. Thus, this method is not efficient.
U.S. Pat. No. 4,261,822 illustrates a drum-like screen that is placed horizontally in a ditch and held partially out of the water by attached legs. It is designed to be transportable. However, it is designed to be used primarily in only irrigation ditches. Although this device is an improvement over the others, it benefits from two advantages of controlled operating circumstances. First, because it is intended for use in irrigation ditches, the movement of water can be controlled. Second, the water level can be controlled. Thus, the strainer may rest on the ditch floor and does not have to be raised or lowered with changes in water level. These conditions are not often found in many bodies of water.